Mobile Circuit Switched (CS) services based on GSM and WCDMA radio access are a world-wide success story. They have allowed telecommunication services to be provided to subscribers in almost all countries of the world with a single subscription. Also today, the number of subscribers to networks that provide CS services is still growing rapidly, boosted by the rollout of mobile CS services in dense population countries such as India and China. This success story has been further extended by the evolution of the classical mobile switching centre (MSC) architecture into a softswitch solution.
However, the amount of data traffic on mobile networks could surpass that of today's broadband connections in the next decade. The Third Generation Project Partnership (3GPP) includes a work item “Evolved UTRA and UTRAN” that includes development of a radio access technology to support anticipated growth in mobile networks. This has been given the name Long Term Evolution of Universal Terrestrial Radio Access Network (UTRAN)—or LTE for short. LTE will use OFDM radio technology in the downlink and SC-FDMA for the uplink, allowing at least 100 Mbps peak data rate for downlink data rate and 50 Mbps for uplink data rate. LTE radio access can operate in different frequency bands and is therefore very flexible for deployment in different regions of the world.
Whereas LTE development focuses on the evolution of the 3G Radio Access Network (RAN), 3GPP also includes a System Architecture Evolution (SAE) work item to develop an evolved core network (CN). This new core network is also called Evolved Packet Core (EPC). Both the LTE RAN and the SAE core network only operate in a Packet Switched (PS) domain, i.e. all services are to be supported via this domain. To date, LTE/SAE can be considered to be service “agnostic”. It does not care about the nature of the data. It has been assumed that services will be facilitated by a service level core network, and in particular by the IP Multimedia Subsystem (IMS).
It appears however that the assumption referred to in the preceding paragraph is not necessarily valid, due to the fact that some LTE/SAE network operators may not wish to implement an IMS network at all, or at least not simultaneously with LTE/SAE deployment. In this case, it becomes imperative that the SAE is able to handle or provide access to at least certain services, and in particular to the traditional CS type services referred to hereafter as legacy CS services.
LTE and SAE are being specified without fully accounting for co-existence with legacy CS services. Existing GSM and UMTS networks provide both PS and CS access simultaneously, and a problem arose in how to provide CS based services in the LTE access networks, particularly where such services have already become well established. Various solutions to this problem have been devised that enable use of LTE/SAE as access technology to the existing infrastructure so that services can be provided using both PS and CS access. These solutions are called “CS over LTE” (CSoLTE) and a preferred basic architecture for these solutions will be described below in relation to embodiments of the invention. Both the IMS CN and the CSoLTE solutions are described in this application as service level networks meaning that the communication towards the terminal and the 3GPP networks is based on the (S)Gi interface and IP (Internet Protocol) based communication.
One requirement for location based services and applications in the existing and new CS and PS core networks and in the service level networks is that the location of the user terminal or mobile station (MS) must be identified on different levels. Two such mechanisms are the Service Area Identifier (SAI) and Cell Global Identity (CGI) which are both used by the RAN to indicate the location of the MS to the CN and then used by the location based services and applications in both the CS and PS parts of the core network. SAI is used to indicate the current Service Area (SA) in which the user terminal or mobile station (MS) is located and the CGI is used to indicate the current cell where the MS is located. The differences between SAs and cells are summarised below and described in more detail later on.
The SA is a concept introduced in the 3GPP standards as part of the standardisation of the UMTS and UTRAN networks. Before this the GSM network used instead the Cell Global Identity (CGI) for similar purposes.
It was decided as part of the UMTS and UTRAN standardisation work in 3GPP that the cell identities are a radio access network (RAN) concept and should not be visible in the CN or communicated from the RAN to the CN. For this purpose the concept of a Service Area was introduced. However, in UMTS networks, the SAI is not known to the MS as only the cell identity is broadcasted in the system information and then mapped to a SAI in the Radio Network Controller (RNC) before being indicated to the CN. The location based services and applications in the UMTS CN are based on usage of SAI to define geographical information.
As the current SA is not known to the MS or to the service level network (e.g. IMS CN or CSoLTE solution), there are problems in providing location based services and applications in these service level networks. In particular, the way that the LTE radio access network and SAE core network communications are configured means that there is no way currently for the RAN (e.g. an eNodeB in LTE or RNC in UTRAN) to provide the current SA of the terminal to the new service level network.
It is an aim of the present invention to alleviate this problem.